[CentOS] Squirrelmail Change Password Plugin Problem

Hi, I have recently setup CENTOS ver.4.4 as our mail server and I have
installed Squirrelmail as our Mail User Agent. Everything seems to be
working fine but I encountered problems in one of the plugins of
Squirrelmail which is the Change Password plugins that changes the
password in the shadow file. The change password function doesn't seems to
work because Squirrelmail replies an error message that does not allow the
change password function to change the password of the users. My first
guess is because of the file security setting and I can't seems to go
around this. One thing I notice though is that when the file is inside the
/var/www/html/ directory, the php scripts that I have tried to edit a file
seems to work but if the file is outside this directory just in the case
of the shadow file which is located at /etc/ directory it doesn't seems to
work or it does not allow the file to be modified. Can you please help
with this? I would really appreciated your help.